In the modern communications space, wireless access networks are increasingly popular, as they enable subscribers to access communications services without being tied to a fixed, wireline communications device. Conventional wireless access network infrastructure (e.g., base stations) is typically “built out”, by a network service provider, using a network-centric approach. Thus the build-out normally begins with major Metropolitan Service Areas (MSAs) using base stations located at the center of overlapping coverage areas or “cells”. The build-out, and corresponding wireless communications services, subsequently migrates outward from the MSAs to areas of lower population/service densities (e.g., urban to suburban to rural, etc.). At some point, usually dictated by economics, the build-out slows and/or becomes spotty leaving many individual wireless subscribers with unreliable or non-existent service.
On-frequency repeaters are known in the art for improving wireless services within defined regions of a wireless network (e.g., within a building or a built-up area). Such on-frequency repeaters are typically provided by the wireless network provider in order to improve signal quality in high noise or attenuation environments, where signal levels would otherwise be too low for satisfactory quality of service. In some cases, a wireless network provider may install a repeater in order to improve service in an area lying at an edge of the coverage area serviced by a base station, thereby effectively extending the reach of the base-station.
Prior art repeaters are part of a network-centric view of the wireless network space, in that they are comparatively large systems provided by the network provider in order to improve wireless service to multiple subscribers within a defined area. As such, they form part of the network “build-out plan” of the network provider. These systems suffer the disadvantage in that an individual subscriber cannot benefit from the improved services afforded by the repeater unless they happen to be located within the coverage area of the repeater. However, there are many instances in which wireless subscribers may reside or work in areas where the coverage area of the wireless network is unreliable. Typical examples include mobile subscribers, and subscribers located in suburban and rural areas. Also, in-building coverage can be unreliable even within MSAs, depending on the size, location and construction of buildings and/or other obstacles. In such cases, it may be uneconomical for a network provider to build-out the network to provide adequate coverage area, thereby leaving those subscribers with inadequate wireless services.
Accordingly, Applicant's co-pending U.S. patent application Ser. No. 09/809,218, filed on Mar. 16, 2001 and entitled Adaptive Personal Repeater, the contents of which are incorporated herein by reference, provides a method and apparatus that enables an individual subscriber to cost-effectively access high quality wireless communications services, independently of the location of the subscriber. The Adaptive Personal Repeater (APR) transparently mediates signaling between a subscriber's wireless communications device (WCD) and a transceiver (base station) of a wireless communications network. The repeater includes a Directional Donor Unit (DDU) and a Subscriber Coverage Unit (SCU). The DDU maintains a network link with the base station of the wireless communications network. The SCU maintains a local link with the WCD within a personal wireless space of the APR. Total system gain is divided between and integrated with the DDU and the SCU, so that a separate gain and system control unit is not required. This division of system gain also enables high-performance on-frequency repeater functionality to be obtained without the use of high-cost components and building blocks.
As described in U.S. patent application Ser. No. 09/809,218, the APR represents a subscriber-centric solution for improving wireless services as required by one or more subscribers, and in a manner that is transparent to the network. However, in order to provide this functionality, it is necessary for the repeater to provide sufficient system gain in each of the uplink and downlink paths to compensate for propagation losses in these paths. On the other hand, if the gain (in either the uplink or downlink paths) is too high, the repeater will radiate unnecessarily high signal powers to the subscriber's WCD and/or the base station. In an environment in which there is more than one APR in use, radiation of excessive signal power in the downlink path can cause interference (in the form of multiple overlapping coverage areas) with other subscribers. The same holds true for a single APR radiating excessive power in the downlink path causing interference to other subscribers outside the personal wireless space. Similarly, radiation of excessive signal power to the base-station may cause interference with other base-stations and/or other users of the wireless communications network.
Automatic Gain Controllers (AGCS) capable of controlling signal gain are known in the art. Typically, AGCs are implemented as analog RF or IF circuits, in which a (voltage controlled) variable gain amplifier (VGA) is used to amplify the analog signal. The VGA is normally controlled by a voltage level of a control signal, which is usually generated (by a comparator) by comparing a measured parameter (e.g., a received signal power, or a bit error rate) to a predetermined threshold value. AGCs of this type are capable of providing reliable operation within the range of linear operation of the VGA. Typically, operation of the AGC becomes increasingly unreliable beyond the linear range of the VGA, and thus the performance of the AGC is typically limited by the linear range of the VGA. However, it is anticipated that successful operation of the repeater will require that system gain be controllable through a range of up to about 120 dB in both the uplink and downlink paths. This range of operation is well beyond the linear range of moderate-cost VGAs.
Another difficulty typically encountered in on-frequency repeaters is system oscillation resulting from imperfect isolation between the two antennas. Conventional on-frequency repeaters normally require that the total system gain must be about 10-15 db less than the antenna isolation in order to prevent oscillation. Typically, antenna isolation and system gain are adjusted by service personnel during installation and set-up of the repeater unit, in order to achieve satisfactory performance. However, this is a labor-intensive operation requiring skilled technicians using specialized equipment. This increases the cost and complexity of installing the repeater, and thereby greatly discourages individual subscribers from acquiring a repeater for their personal use.
Accordingly, a method and apparatus capable of automatically controlling gain throughout a wide operating range, in order to compensate for propagation losses and imperfect antenna isolation, at a moderate cost, remains highly desirable.